The degree to which you come right back in the hospital after you've been discharged;

Situations in which too many imaging tests that expose you to radiation are being done;

Common complications in unsafe hospital; and

Death rates for several conditions.

The lowest-rated hospital in the country, he told "CBS This Morning: Saturday" co-hosts Rebecca Jarvis and Anthony Mason, was Sacred Heart Hospital in Chicago.

"Across the board," Dr. Santa said, "in those six areas, they did not do well. They got many of our lowest or close-to-lowest scores. So they weren't preventing infections. These complications were happening. People (were) getting bedsores, falling. They had problems with doing two CT scans when one would suffice. There were a lot of things they could do better.

"But let me say: The best hospitals didn't do as well as I think they could. And they know that. The best hospitals know we've got to do better. The problem is, not by any means are all hospitals acknowledging that in making this a high priority."

The extent of the problems the magazine found was eyebrow-raising.

"For this story," Dr. Santa explained, "Peter Pronovost, really one of the country's most prominent experts in terms of hospital safety, said he believes (that), if we kept the best track of this, that deaths from safety and error issues in hospitals would be the third most common cause of death in the country."

At the other end of the spectrum from Chicago's Sacred Heart is the Billings Clinic in Billings, Mont. It was ranked as the safest hospital.

"They acknowledge this is hard work," Dr. Santa says, "but they're getting it done. They need to do better. They need to keep making improvements. But they're getting it done. And so are many others."

Some of the best-known teaching hospitals, some big names, didn't fare as well as many people might think.

"A challenge is these are hospitals that have a lot of priorities," Dr. Santa observed. "We have a lot of expectations from them. They do teaching, they take care of tough patients. Our concern is, even for them, safety needs to be the top or near the top priority. Who else will figure this out when it comes to the really complicated stuff? and we're concerned that those really best hospitals are the ones we expect to be best aren't doing as well as we would all think."